1971 454/425hp LS6 Heads - Uncertain Usage?

[David D.]

I have a 1972 454 Block Casting Code 3999289 with 1971 454/425hp cast iron heads casting code 3994026 (uu), Date code F14 71 and D28 71.

In the Corvette Black Book 1953-2003 it indicates that these heads are marked as (uu) = Uncertain usage in 1971. What exactly does "Uncertain usage" mean? How rare are these heads? How many were made?

When I look these heads up on line I find that they are 118cc cumbustion chamber heads and the last of the Mark IV square port/open chamber design and it lists them as LS6 heads. I thought a true LS6 head in 1971 was an all Aluminum head, not Cast iron?

When I look up the casting number for the all aluminum LS6 heads it shows them as 3994025, one digit off from the cast iron heads(3994026) that I have. Can someone help to clear this up for me?

[Clem Z.]

Re: 1971 454/425hp LS6 Heads - Uncertain Usage?

I have a 1972 454 Block Casting Code 3999289 with 1971 454/425hp cast iron heads casting code 3994026 (uu), Date code F14 71 and D28 71.

In the Corvette Black Book 1953-2003 it indicates that these heads are marked as (uu) = Uncertain usage in 1971. What exactly does "Uncertain usage" mean? How rare are these heads? How many were made?

When I look these heads up on line I find that they are 118cc cumbustion chamber heads and the last of the Mark IV square port/open chamber design and it lists them as LS6 heads. I thought a true LS6 head in 1971 was an all Aluminum head, not Cast iron?

When I look up the casting number for the all aluminum LS6 heads it shows them as 3994025, one digit off from the cast iron heads(3994026) that I have. Can someone help to clear this up for me?

from what i under stand these heads were for a still born chevelle 454 engine for 1971. may be they were going to install them on the LS-6 454 450 HP chevelle engine to lower the CR. all the open chamber cast iron heads i ever saw had a casting #672990 and part # 6260482. your heads could also have been sold under the 6260482 part # as they sound like the same heads

[David D.]

Re: 1971 454/425hp LS6 Heads - Uncertain Usage?

Thanks for your reply. I would assume by that information that they did not build many of these heads. Is there any way to determine or approximate the number made?

The engine has a big duration 246-246 and .567 lift cam in it and runs close to 500hp, so the assumption that these heads were originally destined for a LS6 450hp engine makes sense.

[Joe L.]

Re: 1971 454/425hp LS6 Heads - Uncertain Usage?

I have a 1972 454 Block Casting Code 3999289 with 1971 454/425hp cast iron heads casting code 3994026 (uu), Date code F14 71 and D28 71.

In the Corvette Black Book 1953-2003 it indicates that these heads are marked as (uu) = Uncertain usage in 1971. What exactly does "Uncertain usage" mean? How rare are these heads? How many were made?

When I look these heads up on line I find that they are 118cc cumbustion chamber heads and the last of the Mark IV square port/open chamber design and it lists them as LS6 heads. I thought a true LS6 head in 1971 was an all Aluminum head, not Cast iron?

When I look up the casting number for the all aluminum LS6 heads it shows them as 3994025, one digit off from the cast iron heads(3994026) that I have. Can someone help to clear this up for me?

David-----

The term "uncertain usage" or "unverified" in this context refers to the fact that when the spec guide was written there was some question regarding whether, or not, the 3994026 cylinder head was used on 1971 Corvette LS-6 applications. In my opinion, there should have been nothing uncertain about the fact that the 3994026 cylinder head was NEVER used on a 1971 Corvette application. All 1971 Corvette LS-6 cars ever confirmed as original have aluminum heads of casting #3946074. The cast iron 3994026 was not used for any original Corvette application. Ever.

The 3994026 cylinder head was destined for use on 1971 Chevelle LS-6 applications. However, no 1971 Chevelles with LS-6 were ever built. So, any cylinder heads of casting #3994026 manufactured would only have been directed to SERVICE use, either as part of SERVICE engine assemblies or as bare cylinder heads.

Just how many of these heads were manufactured, I do not know. However, as clem mentions, the GM casting #6272990 was, by far, the most common 2.19/1.88 rectangular port, open chamber, 118cc, cast iron cylinder head, and I believe it was released about 1973. If so, I expect that the 3994026 had a "short life" and is probably rare. However, "rare" does not always equal "high dollar". In this case, this cylinder head was never used for any PRODUCTION application so no one would be looking for one for restoration (or "cloning") purposes. As far as performance potential, I can't see the 3994026 being any more desirable than the 6272990 and, likely, less desirable since GM didn't drop the 3994026 in favor of the 6272990 because the 3994026 was better.

I have no knowledge or record of any aluminum cylinder head of GM casting #3994025.

[David D.]

Re: 1971 454/425hp LS6 Heads - Uncertain Usage?

Thank you Joe,
This confirms my comments about all 1971 LS6 engines installed in Corvette's were all aluminum heads. I agree.

I appreciate the additional information as well. My 72 Vette is not an all original car so the modifications don't really hurt the value. I restored it over an 8 month period and aesthetically it appears to be original but a closer look quickly reveals that it is a good daily driver with a lot of horsepower.

Thanks again.
Dave

[Warren F.]

Re: 1971 454/425hp LS6 Heads - Uncertain Usage?

David,

Almost every head that you have usually has a later date than your earlier head. Most I have seen are dated in June of '72. Your April dated head is one of the earlier dates I have noticed. Those heads do not come up often, I believe they are somewhat scarce now. They would have been used on the early over the counter LS-7 engines. That's mostly the applications I have seen these heads on.

[David D.]

Re: 1971 454/425hp LS6 Heads - Uncertain Usage?

Warren,
Thanks for another piece of the puzzle. I'll do a little research on the early LS7's and see what I come up with.
Dave

[David D.]

Re: 1971 454/425hp LS6 Heads - Uncertain Usage?

Where is the three digit "Suffix" located on the engine block?

[Joe L.]

Re: 1971 454/425hp LS6 Heads - Uncertain Usage?

Where is the three digit "Suffix" located on the engine block?

David------


Usually, it's on the engine stamp pad which is an extension of the block forward of the passenger side cylinder head. Sometimes, on later big block SERVICE engines the code will be stamped on a small machined area on the block just above the timing cover.

[Ray K.]

Re: 1971 454/425hp LS6 Heads - Uncertain Usage?

David,

I generally agree with the conversation between you and Clem, Joe, Warren about #3994025 cylinder head for 1971 LS6 engines (425HP / 454 ) but my curiosity was moved so I had to check what info I had. I found in my Chev Corvette P&A 30 catalog dated 9-71 that it actually lists the 3994025 for the 1971 LS6 engines. This head is also referenced in my Chev Special Equipment catalog dated 3-72. We sold this head to engine builders who desired a cast iron head rather than the aluminum open chamber head. This head is also discussed in the "How To Build Big Block Chev Engines" from 11-71. At some point I believe this number was changed to the #6260482 but I don' have a firm date to offer but think it was 1973 /74 era. If all the documented LS6 engines have aluminum heads that is hard proof, but I think the possibility exists that a cast iron head may have been installed for whatever reason.

Ray

[Joe L.]

Re: 1971 454/425hp LS6 Heads - Uncertain Usage?

David,

I generally agree with the conversation between you and Clem, Joe, Warren about #3994025 cylinder head for 1971 LS6 engines (425HP / 454 ) but my curiosity was moved so I had to check what info I had. I found in my Chev Corvette P&A 30 catalog dated 9-71 that it actually lists the 3994025 for the 1971 LS6 engines. This head is also referenced in my Chev Special Equipment catalog dated 3-72. We sold this head to engine builders who desired a cast iron head rather than the aluminum open chamber head. This head is also discussed in the "How To Build Big Block Chev Engines" from 11-71. At some point I believe this number was changed to the #6260482 but I don' have a firm date to offer but think it was 1973 /74 era. If all the documented LS6 engines have aluminum heads that is hard proof, but I think the possibility exists that a cast iron head may have been installed for whatever reason.

Ray

Ray-----


The cataloging of the 3994025 cylinder head for 1971 Corvette LS-6 applications was an error by GMSPO. It was dropped by 1974 with P&A catalogs showing no head for the 1971 Corvette LS-6 application. For 1975, the catalog specified cylinder head GM #3981070 for 1970 Corvette with HD (i.e. LS-7 which was never installed in a Corvette) and 1971 LS-6. The GM #3981070 was an aluminum cylinder head. I do not know what casting this cylinder head used but I expect it was the 3946074. The GM #3981070 was discontinued in March, 1982 and replaced by the GM #14011076 (casting #14011077). The latter was discontinued without supercession in August, 1995.

[Ray K.]

Re: 1971 454/425hp LS6 Heads - Uncertain Usage?

Joe,

Thanks for your response. There is no doubt that there were occasionally errors in the parts catalog, they were usually obvious. However, in this instance I am not convinced that the listing for the #3994025 cyl head was an error for '71 LS6 engine. Do you have a parts bulletin, service update, or some other form of documentation that substantiates your position on this cyl head? I also found the #3981070 listed for the 70-71 engines. It has a dubious history. One of my price catalogs showed it removed from service, but then must have been reinstated later, and then to be discontinued at a later date. I believe also that it probably was #3946074.

Ray

[Joe L.]

Re: 1971 454/425hp LS6 Heads - Uncertain Usage?

Joe,

Thanks for your response. There is no doubt that there were occasionally errors in the parts catalog, they were usually obvious. However, in this instance I am not convinced that the listing for the #3994025 cyl head was an error for '71 LS6 engine. Do you have a parts bulletin, service update, or some other form of documentation that substantiates your position on this cyl head? I also found the #3981070 listed for the 70-71 engines. It has a dubious history. One of my price catalogs showed it removed from service, but then must have been reinstated later, and then to be discontinued at a later date. I believe also that it probably was #3946074.

Ray

Ray------


I have no documentation that the cataloging of the 3994025 cylinder head was an error. However, it seems pretty apparent to me that it was for several reasons:


1) For every Corvette P&A catalog published from 1975 until 1983, the 3981070 (and it's successor GM #14011076) were cataloged as the SERVICE replacement for "1970-71 454 with HD, spec high performance". In those same catalogs, the GM #6260482 was cataloged for "1971 454 with special high performance". So, both the aluminum and cast iron heads were cataloged for 1971 LS-6 at the same time;

2) The GM #3981070 aluminum head was removed from SERVICE in late 1970 and, then, "came back" about 1975 and lasted until it was replaced in March, 1982. So, presumably, during the 1970-75 period there was no big block aluminum head available for the LS-6 and the closest thing that GM had in its parts bin was the 3994025. So, the 3994025 was cataloged as the SERVICE head. From time-to-time, SERVICE parts are different than those used in PRODUCTION and this may have been one of those times.

3) As I mentioned previously, I know of no case in which a 1971 Corvette with LS-6 was ever documented as having been originally built with cast iron heads. Plus, there are only 2 known suffix codes for 1971 Corvette with LS-6 (for the manual and auto trans applications). If there had been engines built with cast iron heads I would expect that different suffix codes would have been used.

[Clem Z.]

Re: 1971 454/425hp LS6 Heads - Uncertain Usage?

the new 1971 LS-1 i worked on owned by john stonick who owned pittsburgh dry wall had the aluminum heads with a THM 400.

[Ray K.]

Re: 1971 454/425hp LS6 Heads - Uncertain Usage?

Joe,

You offer up some very good reasoning about these cylinder heads. And you are correct in that both heads ( cast iron & aluminum ) are listed for the same engine application. That in of itself makes me wonder if in fact engines were produced with both types of heads. If, the #3994025 was service replacement only, there would have been some factory notification to parts and service operations that an aluminum head was not available and therefore to use the cast iron version as a replacement. You then could end with an engine with one aluminum head and one cast iron head. Also, if you verify the engine stamp codes ( CPW & CPX ) in the front of the P&A catalogs the notation for aluminum heads is not present, in every other instance it is listed for the engine code when aluminum heads were supplied. So that makes me think, as you do, there should be special engine codes - cast iron vs aluminum.

Ray